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DOE-HDBK-3010-94
5.0 Surface Contamination; Solid, Noncombustible Surfaces
ARF assessed for suspension from a pile of powder from a hard, unyielding surface due to
accelerated flow generated by an explosion parallel to the surface is 5E-3 with an RF of 0.3
(see subsection 4.4.2.2.2). The stresses upon the surface contaminant, much of which is
embedded in the surface, appear to be fewer than those described for powders on unyielding
surfaces. The stresses are certainly greater than those assumed for the resuspension of
materials from nominal airflow in facilities or outdoors, 4E-5/hr. An ARF of 1E-3 with a
RF of 1.0 was selected for this phenomenon by Mishima, Schwendiman and Ayer (October
1978) in an analysis of severe natural phenomena effects. The ARF value is 20% of the
value assigned for the suspension of loose powders by explosion generated accelerated flows
parallel to the surface and more than an order of magnitude greater than values assigned for
resuspension. On these bases, an ARF of 1E-3 with a RF of 1.0 is assessed to bound the
suspension of surface contamination from non-brittle solid material for this phenomena.
5.3.4
A erod yn am ic E n train m en t an d R esus pen sion
The parameters governing the suspension of particles from a heterogenous surface (e.g.,
metal, some plastic, concrete, glass) are the same as for suspension from a homogeneous
bed; the parameters are the characteristics of the flow, particles and surface. The effects of
the various factors that contribute to the parameters (e.g., aerodynamic lift forces, drag
forces, adhesive forces) vary greatly. Figure 5-2 reproduced from Brockman (February
1985) shows the effect of particle size on various adhesive forces. Figure 5-3 reproduced
from Fromentin (January 1987) illustrates the effect of surface roughness on the
suspendability of small particles. Adhesion decreases with substrate surface roughness until
the macroroughness becomes the same size as the particles, when it increases rapidly
(Hubbe, 1984). The surface roughness of the particles, the presence of moisture, the
plasticity of the surface (Johnson, Kendall and Roberts, 1971), and other factors all appear to
affect the adhesion of particles to substrates or to each other.
Current consensus assumes that flow must be turbulent before significant suspension occurs
(Fromentin, January 1987). This is not necessarily the case for aerodynamic entrainment in
facility ventilation flow or outdoors at windspeeds less than 5 m/s. The turbulent flow is
divided into three regions: 1) core; 2) transition; and 3) viscous sublayer with regions two
and three comprising the wall region (Alonso, Bolado and Hontanon, July 1991). Present
consensus also agrees that turbulent bursts (intermittent ejections of discrete fluid elements
from wall region towards the core) play some role in suspension (Cleaver and Yates, 1973).
The burst process is composed of three steps: 1) deceleration of axial fluid velocity within
local region near wall, 2) progressive acceleration from approach of fluid with mean velocity,
and 3) before affected region totally accelerated, ejection of fluid from region of
unaccelerated fluid. The process is shown schematically in Figure 5-4.
Page 5-24


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